Phosphate metal coatings



Un ed States. Patent PHOSPHATE..METAL. COATINGS;

William S; Russell; Royal Oak, Micl1., assignor to Parker Rush Proof'Company; Detroit; Mieln,v acorporatlom of Michi an .No Drawing.Application August 28', 1952),

Serial o. sop-p61: 12 Claims, (Cl. 148-615) The present inventionrelates to improvedphosphate coating compositionsv and. methods forforming. protective,

phosphate coatings on metallic surfaces including iron steel,.zinc andaluminum. In. particular thisinvention is concerned with animprovedsolution of'the coating-phosphate type, c. g., zinc, iron or manganesephosphate,

It is now well known "that the rate of formation of phosphate coatingson metallic surfaces from solutions of the coating-phosphate type, thatis solutions containing a metallic ion which becomes a part of theintegral coating formed on the surface, is greatly increased by the useof ox-itl-izingor accelerating agents. Typical oxidizing;

agents which have been suggested include nitrates, chlorates, bromates;sulfites, nitrites, perchlorates, periodates, permanganates, etc.Solutions of the CQafi J Phosphafe type operating under conventionalcommercialconditions of continuous production form coatings on, ferroussurfaces usually ranging in coating weight between-about 50 and 600mg./sq ft. For corrosion resistantappliczi tions heavier coatingsaveraging about 160019 mg./sq. ft. are obtained by immersion forrelatively long,

periods of time or by special surface preparation prior cemn eaestrnchelates w th I ethy e e am neetr ce ic. ac r iabi nei; (1th tocoating or both. Heretofore it has not been possible" to producecoatings sufliciently heavy to serve as corrosion-resistant coatings inperiods of timeas low as about. 10 minutes. A

e p incip l i c hep 'esent nvent on s. o Pr vide an improved phosphatecoating solution which" is capable of producing unusuallg l eavyphosphate coatings on metallic. surfaces in short periods of time. I I

Another object is to provide an improved coating solution which producesheavy phosphate coatings on metallic.

surfaces when applied theretoeither by dipping orspray-f ing techniques.p

A further object of the present, invention is to provide a method fortreating the surfaces of iron, steel and zinc to form a heavy phosphatecoating thereon.

Still anotherobjective is to I provide an auxiliary accelerator which incombination with conventional oxidiiing -agents in a coating-phosphatesolution greatly in creases the coating weights obtainable on me'tallicsur faces.

Other objects and advantageous features of the invention will becomeapparent upon considering the present disclosure in its entirety.

In accordance with this. invention, iLhas beenf oundham r d cati nateca-s t e were phosphate type and having a pH in the range of 1.9 to 3.5

I face of the metal being coated. Coating-phosphate solu- V enter:t onalxi z ng g nt Q-h pre nt in: 0

saa s an -1 m:

I 2,743,204 Bate ted Apr. 24, 1956 are unexpectedly accelerated by theaddition thereto of small quantities ofcertain organic chel'ating aggnflertain amino acids, and'parti'cul'arly" alpha "amino acids; such;asglycine, alanine and-,sarcosinei'form coins pleases. with certainmetal ions such as iron, copper; zine; nick l). m. in 8. ion and this;complexingetfectively remotes-- such: ion tom. the olution, or: pr en hi' r m ar y ng. out theta ncrmalrreacticns. Polycarbox-L yliq alphaminosacids, such. as; ethylenediamine tetnm acetioaci have; evengreater tendencies torfornistable metallic ions in comparable: flltiqnfin han. 9 h simpler minqiacidsi. Aqueous: solu ians. atpclycarhcxy ealnha amino acidsne ia kaliaeiuna u eand are known-to.-lose their chelatingaonompl xin b ty ecreasingpH on in otherwo-rds n.easin aodi y= hus, heeatra heavy-coat n we h s. wh wereqbt ine i nd. ued; by: he. addition? b -ED111013; ties of such c; r,ga nicvchelatingiagentsi to relatinely: a inapho phate o utions were; not epected. or he re en sincr a e in. oatineweight s.no -.-co p e elynde stod; Coating wei htaresnlting. from the presence in the coating solutionofiasrnali qnana itles ofi 'pol-y a boxy c amino ac have een. increasebit: as, anch n imes. verhat. whi s btained: undeniden ic tp cc ssing. oitions; except}; ton pres e.

t h mino. a i I ncphosphe es lu icns h r tage- PH, between an 5. heartycoa ing w ights. chem steris ic: of thisin nt on net ob ined n he abence of a. conveat nm ox d z g: a ent: Manganese an hi q Phosphat so uts, o he o he andt'do. notreqn re a. to. ob ain he x ra hea y e t ns jaahett Benedi t t m Or anic; h lati g a e which ha -been te n e par cularys it-able f e pume esz t a" mye ti rta he pe y a-rb xy a pha am o ac dsac t ci t oa Pr duct-Qt m ienisl ndt ie etraac t c. acre-d ri ab c rmethrles d' The hem-t ns. ent maybeadd drtq: e c atiaa ieth Q5? thisiavetionint e f m. at he am n ac s. bus r. al bflityre on t Pref red. at thamiuoacids eemp oy dte I inner salt; as e sodium t h da t. an e ra maybemployed- Sol t o s ha a e usetul t r e. p rpose at th s n ent eaand; thhe general c ass fi ation 1.: coating-phosphate solutions which operatein continuous; PRQQH t K Z s balan d se utions hay n a. PH? b twe 31%?19 3 5+ nslu e hep n tes titineman; S t ens :havms an ro en Queen:centration greater than phi-oi n? have. a tendanceeact as a pickle andto form undesirable pits on the surtions have 1 a. tendency. to; formlarge; quantitiesof inso1uble phosphates commonly called sludge, anclas.the pHB approaches. 3.5 this tendency is greatly accentuated andrenders. the. continuous. operation of the. S0lllti0n;6X-z tremely.diflicult. Maintenance. ofthe. pH-of 'the solution between the. limits.of. 1.9,, and. .3..5 is important andanecesz ary: to. thecc s ul ormat oat the. desi ed heartw 3 TABLE I oxidizing agent: Percent Chlorate.03-5.0 Bromate .03- .5 Nitrite .01-.15 Sulfite .02 .15

Other specific oxidizing agents which may be used are potassium iodate,sodium meta-nitrobenzene sulfonate, picric acid, hydroxylamine, etc.Typical concentrations which may be used are 0.02% to 0.5% potassiumiodate, 0.03% to .5 sodium meta-nitrobenzene sulfonate, 0.01% to 0.3%picric acid and .01 to .3% hydroxylamine. The proportion given for eachoxidizing agent is that proportion which causes a substantiallyequivalent amount of oxidizing or acceleration of the coating formationas 'is caused by any other oxidizing agent when present in the quantityshown. Nitrates may be used in manganese phosphate solutions at aconcentration between 0.1% and 5% and may likewise be used in zincphosphate solutions, although in certain cases they are not the mostbeneficial oxidizing agents with the latter solutions. When usingnitrites it is preferable to maintain the temperature of the solutionbelow about 140 F. inasmuch as the nitrite appears to react with thechelating agent and to decrease its effectiveness.

Increases in coating weight and improved resistance to corrosion havebeen observed to result from the addition of extremely small quantitiesof chelating agent to the coating solutions above described. Quantitiesas low as about .01% of ethylene diamine tetra-acetic acid or equivalentproportions of the tetra, tri or di sodium salts thereof, or oftriglycine or the tetra-acetic acid derivative of trimethylenediamineare beneficial and produce increases in coating weight, and proportionsup to about 3% of ethylene diamine tetra-acetic acid or its equivalentas the salt, may be used. The upper limit is not critical inasmuch asquantities in excess of 3% may be tolerated. The upper limit is usuallydetermined on the basis of economy and ease of operation and proportionsabove about 1% have not been found to be necessary in the majority ofapplications. A few simple tests under operating conditions will easilyestablish the most desirable concentration. For example, in zincphosphate solutions using chlorate as oxidizing agent, the preferredconcentration of ethylene diamine tetra-acetic acid, based on the tetrasodium salt, is in the range of about .1% to about .3%. Proportionsbelow about .01% ethylene diamine tetra-acetic acid have some beneficialeffect, but the effect is not as pronounced as with concentrationsexceeding 0.01%.

The following examples are given to illustrate in detail the improvedcompositions of this invention and the specific method which may be usedin applying these compositions to metallic surfaces.

Example 1 An aqueous solution was made up with the followingcomposition:

The solution operated at a pH of 23-335. Four inch by six inch coldrolled steel panels were cleaned of oil and other foreign material byconventional cleaning methods such as dry wiping followed by wiping inmineral spirits or a short pickle in sulfuric acid. The panels were thenimmersed in a solution of the above composition heated to 160 F.-200 F.for periods of 1, 3, 5, 10 and minutes. Coating weights received were108 mg./sq. ft. after one minute, 110 mg./sq. ft. after three minutesand only 118 ing/sq. ft. after 15 minutes. The solution was then alteredby adding .5 grams/liter of tetra sodium ethylene diamine tetra-acetate.A series of identi- 4 cally cleaned panels were then immersed in the newsolution for l, 3, 5, 10 and 15 minutes. Coating weights obtainedincreased as follows:

The concentration of tetra sodium ethylene diamine tetraacetate wasincreased to .1%, .3%, .5%, 1%, 2% and 3% and a series of panelsimmersed in each solution for comparable time intervals. Coating weightsobtained after three minutes in each of the solutions are as follows:

Coating wt., M n sq. it.

Tetra sodium ethylene diamine tetra-acetate Example 2 Grams/liter Zincdihydrogen phosphate 18 Sodium bromate 5.5

The solution operated at a pH of 2.7-2.9.

Prelimi-narily cleaned cold rolled steel panels were immersed in thesolution heated to about F. for three minutes. Coating weights averaging55 rug/sq. it. were obtained. To the solution was then added 2.5 grams/liter of the tetra sodium salt of ethylene diamine tetraacetic acid, andcoating weights were observed to increase to an average of 313 rug/sq.ft. after otherwise identical treatment.

A series of compositions similar to those of Example 1 and 2 were madeup in which the sodium chlorate and sodium bromate was replaced withother oxidizing agents including sodium nitrate, sodium nitrite, sodiumsulfite, nitrobenzene sulfonate, hydroxylamine, etc. A few of thesevariations are given in the following examples.

Example 3 Grams/liter Manganese dihydrogen phosphate 20 Sodium nitrate10 Triglycine .5 to 30 Example 4 Grams/liter Zinc 3 Phosphoric acid 12Sodium m-nitrobenzene sulfonate 3 Ethylene diamine tetra-acetic acid .4to 27 Example 5 Grams/liter Manganese dihydrogen phosphate 15 Sodiumm-nitrobenzene sulfonate 6 Tetra sodium ethylene diamine tetra-acetate.5-30

am zes Tetmgs di m; ethvhndimie lte r r s tat 3+ -5-. 0

Corrosion resistance of the Coatings appeared to be somewhat better whenthecoatingsfresulted from longer immersion periods, that -is,-;between-- and minutes and the temperature approaehed-"the upper"operating Bumper-bar stock, preliminarily-cleaned, was sprayedfor 6.0seconds incthe above solution at 138 F. Coating. weights obtainedvaried: from 48. to .135 nag/sq ft.- The. SQ JliQ wast-altered byaddingl. 'gram/litenof tetra sodium ethylene diamine tetra acetate. The.solution then had a pH of 2.7 and coating weight after sixty-second p yried between 33.65am, 416 met/sq. ft.

' Examples v 1 Grams/liter Manganese dihydmgenphosphate Tetrasodiumethylene.-diamine tetra a cetate l to 6 Clean .c'old rolled'steel'panels processed inthis. solution.at.205 F. to 210 F. for 10,-minutesshowed over 50% increase in coating weight as the result of adding 1gram/liter of the chelatingagent-over that obtained without=the;.chelating agent. The heavie'stooatingwas' o tained at 3 gramszliter ofthe chelatiug agent.

Portions of this solution were modified by incorporating proportions ofvarious oxidizing agents. within the above given ranges. Optimumconcentrations of tetra sodium ethylene diamine tetra acetate are asfollows:

ox iz n gen per ent. Chelat sagen er 1 ni rate g .1. damn- 025-06 .1nitrite p .03-.,l0 .6 chlorate 0.3-1.0 .6 sodium m-nitro benzenesulfonate 0.1-1.6

A composition particularly useful for treating aluminum or aluminumalloy surfaces is given in Example 10.

Example 10 Pounds Phosphoric acid (75%) 37 Nitric acid, 42 B 71.5 Zincoxide 42.5 Boric acid l8- Hydrofiuoric acid (60%) 16.5 Sodium bifiuoride17 Water to make 500 gallons.

. Y xc ud a Zinnia- 04 Y Grams/liter; 1's NaClOs d 4' Operating'pH-2.5-3.0

a coating having. a, weight of 367- rags. per Square ft. ,Variousportions of the, basic solution were altered by incorporating minorquantities oftetra-sodium ethylene diamine tetra-acetate to produceconeentrati'ons;of'03%, 06%, 11%; 3% and-61%. Increases in coatingweight were observed at each concentrationwith a coating weight of about1",'550 -m gs. per square footioccurri'ng at 6% tetra sodiumethylenefdia-rnine tetrafacetate; Panels; of 24S Tstock werealsotreatedin the alternating'portions of the basic solutionandcomparableincreases: in coatingwei-ght were observed at eachconcentration up to amaximum of about 1,840 mgs. persquare footat' 6%concentration of, tetra sodium ethylene diaminetetraacetate. Then ostdesirable concentration or; tetra sodium'ethylene diamine tetr a acetatein this solution appears to bebetween .3% and.6%

A solution particularly adapted for-coating zinc, galvanized iron or thelike is givenin Example V a The. aqueous. solution .having theabove,analysisis: prefi stably f m d b a m rtqltq i ns oi sa lfi fh oluti n-@503 t fiv mi u e t menve a e coating weight of .445Qmgs pen. square,foot .was,. obtained,

quantities. ot, tetra. ettutlone diamine tetra-acetate.

;6%.-f. Theqoating weightswe gernoted to'increas fr nythg o e t ant t spward a fat. bout 2.65. mgs. per square foot at a concentration of .6%of the tetra s di m. e h e e d smis te ra-amul t ,T e sw m ererating,concentration of tetra. sodi ethylenecliamiue @ua amtat mhtwssw-3t%=and-6%- Whatisclaimedis; I I a 1. ,A. solution for producingvphosphate; coatings on eta l urf e ou stinses s tial fa Phgsphate met cedfi m he rou wast an z n a d. manganese. and an acetic acid, saidsolution having. ajpH'intherange-of-abont.1.9aud 3.5.. v

2. A composition for producing heavy phosphatevcoathuge on,metallic-surfaces inshort periods'of time which consistsessentiallyof anaqueous acidic. solution of a phosphatwt et lf t the ewe s ns fiasqfitqu zinc and manganese, an oxidizing agent and an acetic amino acid,said solution having pH in the range of 1.9 to 3.5.

3. A solution for producing heavy phosphate coatings on metallicsurfaces in short periods of time consisting essentially of an aqueousacidic solution of a phosphate selected from the group consisting ofzinc phosphate, iron phosphate and manganese phosphate, an oxidizingagent selected from the group consisting of nitrates, nitrites,chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, andhydroxylamine, and an acetic amino acid, said solution having a pHbetween 1.9 and 3.5.

4. A solution for producing heavy phosphate coatings on metallicsurfaces in short periods of time consisting essentially of an aqueousacidic solution of a phosphate selected from the group consisting ofzinc phosphate, iron phosphate and manganese phosphate, an oxidizingagent selected from the group consisting of nitrates, nitrites,chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, andhydroxylamine, and at least about .01% of on metallic surfaces in shortperiods of time consisting essentially of an aqueous acidic solution ofa phosphate selected from the group consisting of zinc phosphate, ironphosphate and manganese phosphate, an oxidizing agent selected from thegroup consisting of nitrates, nitrites, chlorates, bromates, sulfites,nitrobenzene sulfonate, picric acid, and hydroxylamine, and a chelatingagent selected from the group consisting of ethylene diaminetetra-acetic acid, triglycine, the tetra-acetic acid derivative oftrimethylene diamine and the alkali metal salts thereof in an amountequivalent to .01% to 3% of ethylene diamine tetra-acetic acid, saidsolution having a pH between 1.9 and 3.5. v

6. A solution for producing heavy phosphate coatings on metallicsurfaces in short periods of time consisting essentially of an aqueousacidic solution of a phosphate selected from the group consisting ofzinc phosphate, iron phosphate and manganese phosphate, an oxidizingagent selected from the group consisting of nitrates, nitrites,chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, andhydroxylamine, and about .01% to about 3% of ethylene diaminetetra-acetic acid, said solution having a-pH between,1. 9 and 3.5.

7. A method which comprises obtaining a corrosion resistantheavy coatingon iron, steel and zinc by subjecting the surface of said metal to theaction of an aqueous acidic solution of a phosphate of a metal from thegroup consisting of iron, zinc and manganese; and an acetic amino acid,the pH of the said solution being between 1.9 and 3.5

8. A method which comprises obtaining a heavy, corrosion resistantcoating on a metal selected from the group consisting of iron, steel andzinc by subjecting the surface of said metal to the action of an aqueousacidic solution of a phosphate selected from the group consisting ofzinc phosphate, iron phosphate and manganese phosphate, an

oxidizing agent selected from the group consisting of ni-,

trates, nitrites, chlorates, bromates, sulfites, nitrobenzene sulfonate,picric acid, and hydroxylamine, and an acetic amino acid, saidsolutionhaving a pH between 1.9 and 3.5.

9. A method which comprises obtaining a heavy, corrosion resistantcoating on a metal selected from the group consisting of iron, steel andzinc by'subjecting the surface of said metal to the action of an aqueousacidic solution of a phosphate and manganese phosphate, an oxidizingagent selected from the group consisting of nitrates, nitrites,chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, andhydroxylamine, and at least about .0l% of ethylene diamine tetra-aceticacid, said solution having a pH between 1.9 and 3.5.

10. A method which comprises obtaining a heavy, corrosion resistantcoating on a metal selected from the group consisting of iron, steel andzinc by subjecting the surface of said metal to the action of an aqueousacidic solution of a phosphate selected from the group consisting ofzinc phosphate, iron phosphate and manganese phosphate, an oxidizingagent selected from the group consisting of nitrates, nitrites,chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, andhydroxylamine, and a chelating agent selected from the group consistingof ethylene diamine tetra-acetic acid, triglycine, the tetra-acetic acidderivative of trimethylene diamine and the alkali metal salts thereof inan amount equivalent to .01% to 3% of ethylene diamine tetraacetic acid,said solution having a pH between 1.9 and 3.5.

11. A method which comprises obtaining a heavy, corrosion resistantcoating on a metal selected from the group consisting of iron, steel andzinc by subjecting the surface of said metal to the action of an aqueousacidic solution of a phosphate selected from the group consisting ofzinc phosphate, iron phosphate and manganese phosphate, an oxidizingagent selected from the group consisting of nitrates, nitrites,chlorates, bromates, sulfites, nitrobenzene sulfonate, picric acid, andhydroxylamine, and about .01% to about 3% of ethylene diaminetetra-acetic acid, said solution having a pH between 1.9 and 3.5.

12. A composition for producing heavy phosphate coatings on metallicsurfaces in short periods of time which consists essentially of anaqueous acidic solution of a phosphate of a metal from the groupconsisting of iron, zinc and manganese, an oxidizing agent, a fluorideand an acetic amino acid, said solution having a pH in the range of 1.9to 3.5.

References Cited in the file of this patent UNITED STATES PATENTS1,911,726 Tanner et al. May 30, 1933 2,132,883 Romig Oct. 11, 19382,298,280 Clifford et a1. Oct. 13, 1942 2,316,811 Romig Apr. 20, 19432,461,519 Bersworth Feb. 15, 1949 2,479,423 Snyder Aug. 16, 1949 FOREIGNPATENTS 663,650 Great Britain Dec. 19, 1949 OTHER REFERENCES .TheProperties and Uses of Ethylenediamine Tetra Acetic Acid and Its Salts,published 1949 by the Bersworth Chemical Co., Framingham, Mass. Page 7is particularly pertinent.

The Modern Chelating Agent, published 1949 by the Bersworth ChemicalCo., Framingham, Mass. Pages 1, 8-11 and 13 are pertinent.

1. A SOLUTION FOR PRODUCING PHOSPHATE COATINGS ON METALLIC SURFACESCONSISTING ESSENTIALLY OF A PHOSPHATE OF A METAL SELECTED FROM THE GROUPCONSISTING OR IRON, ZINC AND MANGANESE, AND AN ACETIC AMINO ACID, SAIDSOLUTION HAVING A PH IN THE RANGE OF ABOUT 1.9 AND 3.5.